Recent advances in hierarchical three-dimensional titanium dioxide nanotree arrays for high-performance solar cells

Hierarchical metal oxide nanotree array architectures with tunable three-dimensional (3D) morphologies and homo-/heterogeneous junctions, consisting of 1D/2D nanobranches grown epitaxially on the sidewalls of vertical 1D nanostructured trunks (resembling a tree), have been widely explored to demonstrate their huge potential in the development of high-performance photovoltaic devices. In this review, the growth of a wide variety of TiO 2 nanotree array architectures will be discussed, with an emphasis on solution-phase and vapor-phase syntheses. The evolution of electrode materials and recent progress in 3D TiO 2 nanotree array architectures for solar cells are reviewed. Furthermore, to highlight the obvious benefits of 3D TiO 2 nanotree arrays, the limitations and challenges of these hierarchical array architectures when used in solar cells are addressed. Finally, insight into future directions and opportunities for these fascinating electrode materials in creating a new energy conversion epoch is also provided. This review article highlights recent progress in three-dimensional hierarchical TiO 2 nanotree array-based high-performance solar cells.